"She definitely had anger problems. She had a lot of hate. Her brain couldn't process it normally," Avanesian said.

Local officers and FBI agents rushed to the video website's San Bruno offices after receiving a string of 911 calls about an active shooter around 12:45 p.m.

A 36-year-old man was taken to the San Francisco General Hospital in critical condition, a hospital spokesman said. Two women, 32 and 27, were taken to the same hospital in serious condition. A fourth person twisted their ankle while scrambling to escape the chaos.

Law enforcement sources initially said they were investigating the shooting as a domestic dispute. San Bruno police later said there was no evidence to suggest Aghdam "knew the victims of this shooting or that individuals were specifically targeted."

Aghdam's rampant social media presence suggested she had a personal vendetta against YouTube.

Nasim Aghdam in a Facebook video dated May 2017. (Facebook)

She accused the video giant of filtering her videos "to keep them from getting views" on her website. Within minutes of her name surfacing in news reports, her YouTube channel was removed.

The site replaced her profile with a red banner announcing the removal: "This account has been terminated due to multiple or severe violations of YouTube's policy against spam, deceptive practices, and misleading content or other Terms of Service violations."

Most of the videos on her profile celebrated her vegan diet.

YouTube employee Dianna Arnspiger said the shooter was armed with a "huge pistol" and wore glasses and a scarf.

"I just said, 'Shooter,' and everybody started running," Arnspiger said. "It was terrifying."

Advertisement

Police officers and crime scene tape are seen outside of the YouTube headquarters following an active shooter situation Tuesday. (Elijah Nouvelage/REUTERS)

A string of similar mass shootings have shocked the nation in recent months, but Tuesday's bloodshed differed in that it was carried out by a woman.

"This is obviously very unusual," Jeff LeDuff, a retired chief of the Baton Rouge Police Department, told the Daily News.

LeDuff said he only oversaw one "active shooter" case involving a female suspect during his 30 years in law enforcement.

He speculated that the increasing rate at which these type of shootings happen is laying ground for a disturbing trend.

"We can't just categorize shooters as one type of person anymore," LeDuff said. "It becomes an option for any deranged individual."